Gender, geography and socio-economic status in the diffusion of malignant melanoma risk.
Malignant melanoma is the cancer that has shown the fastest increase in incidence in most white populations in recent decades. This paper studies the diffusion of the disease for males and females, geographical areas and socio-economic groups. Incidence data from the Norwegian Cancer Registry covering the period 1955-1989 make it possible to establish birth cohorts covering a time span from the late 1880s to the late 1950s. For Norway as a whole the increase in incidence was apparent between cohorts born in the 1880s and the 1890s for both sexes. The epidemic was first observable in the most central, south-eastern part of the country, with the onset reaching the most peripheral Northern Norway from the cohort born in the late 1910s. The onset also came later in rural than urban Norway. There are indications that the epidemic started in the more affluent part of the population, followed by an equalization. The increase in melanoma could be a result of more active outdoor recreation from the end of the last century. In cohorts born from the 1930s onwards a slowing down in the increase can be observed. International comparisons show that in most countries the incidence pattern in the first decades of the epidemic was dominated by males; later on the incidence became higher for females. Many cancer registries in the U.S.A. and Oceania now show a downward trend in melanoma incidence for males and females aged 15-29 years. A similar development has not been observed in Europe and Canada up to 1983-1987.